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Showing 1076 to 1100 of 3046 questions (page 44 of 122).

1076. Cobalt 60 is used in medicine mainly as a source of

A. neutrons B. alpha particles C. beta particles D. X-rays E. gamma rays for radiotherapy

1077. A radioactive sample of initial activity A0 has a half life T. Its activity after time 4T is

A. A0/4 B. A0/8 C. A0/32 D. A0/16 E. A0/2

1078. The molar mass of carbon dioxide is

A. 28 g mol-1 B. 44 g mol-1 C. 12 g mol-1 D. 32 g mol-1 E. 48 g mol-1

1079. One atomic mass unit is equal to

A. 1.6 x 10^-19 kg B. 6.02 x 10^-23 kg C. 9.1 x 10^-31 kg D. 1.661 x 10^-27 kg E. 1.661 x 10^-24 kg

1080. The total number of atoms in one mole of methane is

A. 6.02 x 10^23 B. 3.01 x 10^24 C. 2.41 x 10^24 D. 5 x 10^23 E. 1.204 x 10^24

1081. The molecular formula of a compound is related to its empirical formula by

A. multiplication by a whole number B. division by a whole number C. addition of a constant D. subtraction of hydrogen E. the ratio of densities only

1082. Percentage yield is calculated as

A. actual yield minus theoretical yield B. moles of product times 100 C. actual yield divided by theoretical yield times 100 D. theoretical yield divided by actual yield times 100 E. mass of reactants divided by mass of products

1083. Distillation under reduced pressure is used for liquids that

A. form no vapour B. decompose at their normal boiling points C. have very low boiling points D. are highly volatile E. are immiscible with water

1084. A desiccator is used to

A. heat substances strongly B. weigh precipitates C. dissolve solids D. keep substances free from moisture while cooling E. distil liquids

1085. A sharp and constant melting point is used as a criterion of

A. purity B. conductivity C. density D. volatility E. solubility

1086. In descending paper chromatography, the solvent moves

A. upwards by capillary action B. horizontally only C. in a circle D. in the vapour phase only E. downwards under gravity

1087. At constant volume, the pressure of a fixed mass of gas is directly proportional to its

A. number of collisions only B. density C. absolute temperature D. volume E. molar mass

1088. The volume occupied by 2 moles of an ideal gas at STP is

A. 44.8 dm3 B. 24.0 dm3 C. 11.2 dm3 D. 22.4 dm3 E. 5.6 dm3

1089. Real gases deviate most from ideal behaviour at

A. high temperature and high pressure B. low temperature and high pressure C. high temperature and low pressure D. low temperature and low pressure E. standard conditions

1090. For an ideal gas, the compressibility factor Z is

A. 1 C. greater than 1 always D. equal to the pressure E. less than 1 always

1091. Plasma differs from an ordinary gas in that it consists largely of

A. neutral atoms B. solid particles C. ions and free electrons D. molecules only E. liquid droplets

1092. Evaporation of a liquid causes cooling because

A. the density increases B. the liquid absorbs cold from the air C. the pressure increases D. the volume decreases E. the fastest molecules escape, lowering the average kinetic energy of those left

1093. London dispersion forces become stronger as

A. the molecule becomes smaller B. molar mass decreases C. temperature increases D. molar mass and polarizability increase E. the molecule becomes more polar

1094. The property of crystals by which physical properties differ along different directions is called

A. isotropy B. polymorphism C. isomorphism D. cleavage E. anisotropy

1095. Two substances with the same crystalline form and analogous chemical formulae are said to be

A. isotopic B. isomorphic C. polymorphic D. amorphous E. allotropic

1096. The total number of orbitals in the shell with n = 2 is

A. 2 B. 9 C. 8 D. 4 E. 3

1097. For l = 2, the number of permitted values of the magnetic quantum number is

A. 5 B. 3 C. 7 D. 1 E. 2

1098. The Pauli exclusion principle states that no two electrons in an atom can have

A. the same spin B. identical values of all four quantum numbers C. the same energy D. the same orbital E. opposite spins

1099. The neutron was discovered by

A. Millikan B. J J Thomson C. Rutherford D. Chadwick E. Bohr

1100. The lines in the hydrogen emission spectrum arise when electrons

A. fall from higher to lower energy levels B. are shared between atoms C. move from lower to higher energy levels D. collide with the nucleus E. are ejected from the atom

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